Exemplary embodiments of the present invention relate to a method for producing a surface structure with a lightning strike protective system. In addition, the invention relates to a vehicle component manufacturing method for producing a component of a vehicle using the surface structure production method for providing a surface structure of this component. Finally the invention relates to a surface structure that can be produced with such a method; and the invention relates to a vehicle component exhibiting such a surface structure.
The invention relates, in particular, to the production of layer systems for protecting components against lightning strikes. In particular, such components are used in aeronautical and aerospace engineering, for example, in airplanes or helicopters. However, the surface structures according to the invention can also be used in other vehicles or in other objects that may be exposed to lightning strikes, such as buildings or wind power plants.
Known layer systems are disclosed, for example, in U.S. Pat. No. 4,155,896 and in German patent document DE 10 2006 046 002 B4. The latter German patent application also discusses in detail the technological background of lightning strike protective systems. For more details on this technological background reference is made explicitly to German patent document DE 10 2006 046 002 B4 and the entire state of the art cited therein.
Components made of synthetic plastic material or components containing plastic structures suffer from the problem of providing adequate protection against lightning strikes. For example, such plastic structures in the form of plastic composite materials are used in aeronautical engineering. Composite materials made of synthetic plastic materials, in particular carbon fiber-reinforced plastics (CFRP), have the advantage that they are lightweight and yet have very good mechanical properties, such as a high strength. They can also be made into unusual irregular shapes with ease. Therefore, the use of such fiber reinforced composite materials is promising, in particular, for aeronautical engineering, where it will be used in the future to a greater extent.
The planned use of larger structures in a CFRP type of construction in aeronautical engineering requires, among other things, effective protection against a lightning strike. When lightning strikes CFRP structures, the physical processes are analogous to those with respect to metallic structures. At first a pre-discharge forms a plasma channel and then in the subsequent phase a lightning bolt is discharged. Depending on the location of the first contact point, the lightning channel is drawn over the surface of the aircraft. When the lightning channel makes contact with the aircraft surface, a high current flow and heat input are conjoined in the respective structure. The parameters, which characterize the intensity of the lightning bolt, do not differ between the CFRP structures and metallic components. Since the thermal conductivity and the electrical conductivity of CFRP structures are considerably less than those of metals, it is advantageous to provide CFRP structures, which are to be employed in the external environment, with a lightning strike protective system. Otherwise, when lightning strikes, the net result could be a considerable amount of delamination and, associated with this delamination, a loss of strength.
FIG. 7 shows a surface structure 10 in the form of a layer system 12 according to the state of the art that is currently put into practice in airplanes. The layer system 12 comprises a support structure 14 based on a fiber reinforced synthetic plastic material, in particular a support structure 14 with a CFRP structure 16. In practice, the current trend is to use almost exclusively lattice structures and reticulated structures made of metal in order to protect such CFRP structures against damage from lightning strikes. For this purpose FIG. 7 shows a copper wire mesh 18, which is embedded in a plastic matrix 20 made of the same synthetic plastic material as the CFRP structure 16. According to this figure, a lattice structure or a reticulated structure made of metal is laminated into the CFRP structure 16 as the outer layer, over which a surface film composed of a finish top coat 22 is applied.
Especially in the case of larger structural components, the production of such known layer systems 12 constitutes a time consuming method that is technically complicated and expensive and associated with a significant amount of dead weight.
One example of a similar surface structure is disclosed in U.S. Patent Application Publication No. 2011/0174522 A1 , which relates to a prepreg formed by non-conductive fibrous structures and a fabric structure made of conductive fibers. The fibers are embedded in resin, and a composite component can be constructed from such a prepreg.
A similar surface structure is disclosed in U.S. Patent Application Publication No. 2007/0141927 A1. In this case an insulator layer is placed on a support structure 20; and a metal mesh material, such as an expanded aluminum foil, is placed on said insulator layer; and then the surface is covered with fillers and finishers, such as finish top coats.
In contrast, U.S. Patent Application Publication No. 2009/0227162 A1 discloses a method for mixing particles, such as metal particles, together with nanofibers and nanotubes into finish top coats or paints, in order to produce in this way electrically conductive surface structures on fiber-reinforced composite materials by means of spray application. In another embodiment electrically conductive layers are embedded, as required, into matrix materials as foils or structures that resemble paper or as felt structures; and these prefabricated structures are then placed on the fiber-reinforced composite materials.
Contrary to the approach above, the structures according to U.S. Pat. No. 4,155,896 are provided with conductive layers in that aluminum fibers are admixed in finish top coats or the like and are then oriented in an electric field.
In the aforementioned documents the lightning strike protection is to be achieved solely by providing electrically conductive layers that are supposed to distribute the energy. This solution has not proven to be sufficient in all cases.
German patent document DE 10 2006 046 002 B4 describes a remedy for this problem. In the case of the layer structure that is known from this German patent document, polarizable and electrically conductive elongated particles are embedded in the surface film, where these particles are oriented in the thickness direction, in order to serve as lightning triggering elements. For more details of this approach, reference is made to German patent document DE 10 2006 046 002 B4.
The orientation is necessary in order to achieve sufficient protection against lightning strikes.
The method for preparing such a lightning strike protective system includes that first the finish top coat is mixed with the particles and then applied onto the support structures. While the paint is still fluid, an electric field is applied in order to orient, as required, the polarizable particles in the thickness direction of the layer. The application of an electric field that is strong enough for the complete orientation of the particles is both problematic and expensive, in particular, for complicated surface structures. The desired orientation can be achieved to some extent only inadequately and with difficulty.
Therefore, exemplary embodiments of the present invention provide a method for producing surface structures with lightning protection in such a way that the method is easier to carry out and can be achieved with an improved lightning strike protective system.
The invention provides a method designed for producing a surface structure with a lightning strike protective system and that comprises the steps:
a) providing a support structure based on a fiber-reinforced composite material;
b) applying at least one arrangement of a lightning strike protective material made from or with a conductive material onto the support structure so that the lightning strike protective material arrangement adheres to the support structure in such a way that it is held securely in its position;
c) applying a cover material in such a way that it embeds the at least one arrangement of a lightning strike protective material that is held securely in its position on the support structure; and
d) solidifying the cover material that is applied.
In accordance with the invention the arrangement of a lightning strike protective material is formed by an arrangement of electrically conductive particles as lightning triggering elements that are held securely in their position on the support structure prior to the embedding in the covering material.
By applying the lightning strike protective system before the cover material, which embeds the lightning strike protective system, the desired distribution, arrangement and/or configuration of the lightning strike protective material can be achieved and fixed in position. Then the application and solidification of the cover material appropriately embeds the desired arrangement of a lightning strike protective material and stabilizes the arrangement.
The arrangement of the lightning strike protective material is composed of individual particles that are intended to act, for example, as the lightning triggering elements. At the same time these particles and their distribution can be pre-fixed, as required. This pre-fixing allows at least one end of the particles to be already correctly fixed in position, so that the orientation of the particles can be correspondingly better predefined.
The cover material lends itself preferably to forming an outer surface film that is suitable against environmental factors. For example, the cover material may be a preferably highly stable thermoplastic material. In a preferred embodiment a polyether ketone, for example, as a polyether ether ketone (PEEK), is used as the cover material. Such materials are easily capable of being shaped, on the one hand, and, on the other hand, can be applied in a liquid state, and yet are sufficiently temperature stable and weatherproof as well as resistant to external mechanical impact.
Preferably the lightning strike protective materials, which are formed as particles, of the arrangement of lightning strike protective material are glued directly or indirectly onto the support structure. The lightning strike protective materials can be connected conductively and can be connected to a conductive structure, in particular for dissipating the voltages. In order to trigger the lightning strike, isolated particles, for example polarizable particles, are also suitable according to the discussion of the technological background that is presented in German patent document DE 2006 046 002 B4. Therefore, the particles can also be completely surrounded by non conductive materials.
Based on the aforesaid, one advantageous embodiment of the method provides that step b) comprises:
b1) gluing the at least one arrangement of a lightning strike protective material by means of an adhesive onto the support structure.
Step b1) includes, according to another advantageous embodiment:
b1a) applying the adhesive on the support structure over a wide area, in order to form a continuous adhesive surface, or
b1 b) applying the adhesive on the support structure in certain regions, in order to form a plurality of adhesive areas, or
b1 c) applying the adhesive on the support structure at certain points.
Additional embodiments are characterized by the fact that the adhesive that is to be applied in step b1) is an electrically conductive adhesive or an electrically non-conductive adhesive.
The particles may be polarizable particles. Preferably the particles are oblong. For example, the particles may be formed by fibers, in particular short fibers, and even more particularly by carbon fibers. Another possibility would also be small tubes, such as nanotubes, in particular carbon nanotubes. However, it is also possible to use filaments, such as silicon carbide filaments, graphite filaments or metal filaments or to use pin shaped particles, such as metal pins. If filaments are used, then they have preferably at least one pointed end that has to be directed away so that said end projects from the support structure.
In another embodiment the arrangement of a lightning strike protective material can also be produced by spraying individual metal pins onto the support structure.
The metal pins can be produced, for example, from any suitable metal powder, such as, in particular, aluminum powder.
The arrangement of a lightning strike protective material is applied preferably to a CFRP structure as the support structure.
Based on the aforesaid, a preferred embodiment of the method provides that step a) comprises the production of a two-dimensional flat component substrate from a CFRP composite material, in particular, an epoxy resin reinforced with carbon fibers.
It may be advantageous to provide a protective layer, in particular against exposure to temperature conditions, between the arrangement of a lightning strike protective material and the support structure. This protective layer can be formed, for example, by a felt made of conductive fibers and/or non conductive fibers.
Preferably, the intermediate layer comprises a non-woven fibrous structure.